The 20 best spy novels of all time

This is a book that demands to be read twice in quick succession: once, quickly, to find out what happens; then again, more slowly, to luxuriate in Conrad’s incomparable sentences. (Most subsequent spy writers were perhaps wise to keep their prose fairly functional.) The agent of the title is the seedy porn shop owner Verloc, who is ordered by a foreign power to blow up Greenwich Observatory, although, in a le Carré-ish twist, the purpose of this terrorist outrage is to frame a group of anarchists. Its ending may be the saddest and most savagely ironical of any in fiction.